Regensburg 2019 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 4: Focus: Whispering-Gallery-Mode Resonators
KFM 4.3: Vortrag
Montag, 1. April 2019, 10:20–10:40, H47
Electro-optic tuning of whispering gallery resonators made of KTN crystals — •Ingo Breunig1,2, Jan Szabados1, and Karsten Buse1,2 — 1Laboratory for Optical Systems, Department of Microsystems Engineering - IMTEK, University of Freiburg, Georges- Köhler-Allee 102, 79110 Freiburg, Germany — 24Fraunhofer Institute for Physical Measurement Techniques IPM, Heidenhofstraße 8, 79110 Freiburg, Germany
The electro-optic response of most centrosymmetric materials is neglected. Due to their symmetry, the Pockels coefficients are zero. The DC-Kerr coefficients are typically of the order of 10−22 m2/V2, i.e. very small. Consequently, refractive-index changes in centrosymmetric materials are induced by changing the temperature or by applying mechanical stress. However, potassium tantalate niobate crystals (KTN) operated at temperatures close to the paraelectric-ferroelectric phase transition provide DC-Kerr coefficients in the 10−15 m2/V2 range. Thus, although the material is centrosymmetric, it exhibits a strong electro-optic response. We have fabricated a millimeter-sized whispering gallery resonator made of KTN with a quality factor beyond 107 at 1 µm wavelength. By applying an electric field between its top and bottom surfaces, the eigenfrequencies of the cavity are shifted due to the DC-Kerr effect. For moderate field strengths of 250 V/mm, we achieve more than 100 GHz tuning. This exceeds the value reached with lithium niobate crystals by more than one order of magnitude. The results obtained here are of relevance for the realization of electro-optically tunable adiabatic frequency converters or Kerr frequency combs.